This invention relates to a marine propulsion system, and more particularly to a thrust bearing system for a rotatable propeller shaft employed in a marine propulsion system.
In a conventional marine propulsion system, the gearing and clutch mechanism ar arranged such that clockwise rotation of the propeller shaft, and therefore of the propeller, results in forward thrust which moves the boat in a forward direction. During such forward operation, the thrust created by the propeller is transferred to the propeller shaft, which is typically used to seat the forward driving gear in its bearing cup in the forward end of the gearcase cavity. An axial forward force on the propeller shaft results from the forward thrust created by the propeller.
In some situations, it is necessary or desirable to employ a counterrotation system wherein the propeller blades are pitched so as to provide forward thrust during counterclockwise propeller shaft rotation. For example, in a dual drive installation, the two propellers rotating in opposite directions provide substantially cancelling propeller reaction torques, resulting in improved operation and handling. In a counterrotation drive system, the axial force in the propeller shaft cannot be used to stabilize the forward driving gears as is done in a right-hand rotation system. In essence, the propeller shaft axial thrust stop must be decoupled from the driving gears when the direction of input torque to the gearcase is the same as in a right-hand rotation unit.
To address this problem, a separate thrust bearing system is provided for absorbing the axial forces on the propeller shaft. In a typical prior art thrust bearing system, a circumferential flange is provided on the propeller shaft, and needle bearings are disposed on either side of the flange. A bearing adapter member, including a rearwardly facing bearing surface, is placed adjacent the forward gear needle bearing. A thrust washer is placed against the forward end of the bearing adapter member. A spacer and a thrust ring are provided between the thrust washer and an inwardly projecting lip formed on the walls of the cavity. These components serve to transfer axial forward forces on the propeller shaft to the gearcase. A bearing carrier member, including a forwardly facing bearing surface, is adapted for placement adjacent the rear needle bearing. The end portion of the cavity side walls is threaded, and is adapted to receive an externally threaded ring nut which bears against the end of the bearing carrier member to retain the system in place within the cavity. The bearing carrier member and the ring nut serve to transfer axial rearward forces on the propeller shaft to the gearcase.
The above described construction provides a highly satisfactory bearing system. However, the circumferential propeller shaft flange presents some difficulty, in that the flange is typically either formed integrally with the propeller shaft, or comprises a collar placed on the propeller shaft by means of snap rings. In the former situation, the propeller shaft must be formed from large diameter stock, which increases the cost of the shaft. In the latter situation, the snap rings can experience unsatisfactorily high stresses during operation.
Further, assembly difficulties are encountered due to the diameter of the propeller shaft flange relative to the internal diameter of the propeller shaft cavity. During some steps in assembling the gearing, clutch and shifting components, it is necessary or desirable to tip the shaft in order to attain necessary clearance or the like. With the gear in the torpedo nose supported by a different bearing arrangement and the flange in place, such tipping of the propeller shaft is impossible to accomplish. Then, too, the drive pinion could not be slid past the flange and installed into its pocket. Further, the presence of the flange on the propeller shaft made it impossible to use a crank-type shift system.
The present invention has as its object to alleviate the above-noted problems, and to provide a simplified bidirectional thrust bearing assembly. In accordance with the invention, the propeller shaft flange described above is eliminated. In its place, the propeller shaft is provided with a recess, which preferably extends about the entire circumference of the propeller shaft. In a preferred embodiment, the recess is semicircular in cross section. A pair of force transferring members are adapted for placement within the recess, including an inner surface for placement within the recess and an outer surface which projects outwardly of the outer surface of the propeller shaft. The force transferring members are preferably a pair of semicircular members which, when placed within the propeller shaft recess, substantially encircle the propeller shaft. Front and rear bearing collars are provided, each of which includes a surface adapted to engage the outer surface of the force transferring members projecting outwardly of the propeller shaft. The front and rear bearing collars are preferably adapted for side-by-side placement. The front bearing collar bears against the forward needle bearing, and the rear bearing collar bears against the rearward needle bearing. The bearing adapter and the bearing carrier are substantially identical in construction to that described above in the prior art system, for absorbing forward and rearward thrust in the propeller shaft and transferring forces therefrom to the gearcase housing.